The impacts of FSH and LH treatments on final growth of dominant follicle in a timed artificial insemination protocol in beef Zebu cows

Abstract

Gestational success in cattle depends on several factors, one of which is the diameter of the dominant follicle at the moment of fixed time-artificial insemination (FTAI), thus, the need for strategies to increase follicular diameter in bovine females is evident to increase the results, such as the use of eCG in protocols of TAI. However, in the United States this hormone is not commonly used, where supplementing females with a combination of FSH and LH may be a beneficial eCG replacement strategy for the American beef cattle industry. In view of this, the central thesis of the project is that the association of FSH and LH improves follicular diameter, ovulation rate, estrus expression and pregnancy per FTAI (P/FTAI) in calving beef cows resulting in greater reproductive efficiency. Thus, the main objective is to evaluate the effects of these gonadotropins in ovulation synchronization protocols, analyzing dominant follicle diameter, estrus expression, estradiol, LH and progesterone concentrations and P/FTAI in calving beef cows. For this, on the present Study, 100 Brahman calved cows will receive a PGF2a 6-day CIDR protocol and be randomly distributed in four experimental groups: Control group (n = 20; no additional treatment); FSH-group (n = 20; injection of 20 mg of FSH [Folltropin, i.m; Bioniche, Canada] on day -3; where day 0 = moment of FTAI); LH-group (n = 20; injection of 150 mcg of LH [Lutropin, i.m; Vetrepharm Canada] on day -0,5); FSH+LH-group (n = 20; injection of 20 mg of FSH on day -3 and 150 mcg of LH on day -0,5). Blood samples will be collected in specifics moments and the monitoring of the growth of the dominant follicle will happen until its moment of ovulation, in addition, it will be evaluated estrus expression and P/FTAI. The innovative method here proposed will enable the acquisition of new knowledge about the reproductive physiology of the bovine female and increase the reproductive efficiency in the United States, country that do not use eCG, resulting in a greater number of calves born per year, optimizing the areas of the American livestock. (AU)